This invention relates to absorbent articles and more particularly to layered disposable articles used, for example, as diapers, adult incontinence briefs and sanitary pads, in which a porous liquid absorbing layer of nonwoven fabric or porous film is disposed against the body of the user, and an inner layer is provided for absorption of liquids.
As originally designed, layered absorbent articles have included an inner or body facing cover of a porous fabric, an inner liquid absorbing layer or core, and an outer layer of liquid impervious film. In early products, the core was composed entirely of cellulose wadding or pulp, with the bulkiness or dry weight of the core being directly related to the maximum liquid absorption capacity.
More recently, proposals have been advanced to reduce the bulk of the core and to reduce the overall thickness of the absorbent product for several reasons, such as reduced shipping cost and storage space, and better conformability of the absorbent article or garment to the body of the user. A reduced absorbent core thickness has been accomplished primarily by increasing the density of the absorbent core and by adding up to about 40% by weight of a superabsorbing polymer, the latter being capable of absorbing many times of its weight of liquid. These changes, however, have inevitably led to a reduction in rate of absorption of liquid into the core, resulting in possible runoff and leakage of liquids.
In order to minimize the problems of runoff and leakage in low bulk absorbent articles, additional proposals have been made to employ a high bulk fabric as the upper layer, or to incorporate a transition layer of nonwoven fabric between the outer layer and the core. The purpose of this layer, also known as a sublayer or surge layer, is to hold or retain excess liquid for a time sufficient to allow the core to permanently absorb the liquid.
Various types of fabrics have been used as sublayers, including spunbonded fabrics and fabrics made of adhesively bonded fibers. Another type of fabric used for this purpose is low density lofty fabric having a high liquid void volume. These lofty fabrics, typically have a porosity of greater than 97 percent and are made from through-air thermally bonded bicomponent fibers to provide a sublayer having a high void volume.
In addition to liquid holding properties, another important criteria of a sublayer is to minimize a phenomena called rewetting. Rewetting occurs when liquid held in the sublayer or core migrates back through the porous cover or body side layer under normal contact pressures to wet or hydrate the surface of the skin. Because of their high porosity, lofty fabrics as described above tend to have poor rewet properties and also tend to add bulk to the product. It is well known that absorbent products which have a wet surface in contact with the skin can cause rashes and other skin irritations.
In view of the foregoing considerations, there is a continuing need to provide layered absorbent articles of the compact type which are not only capable of retaining liquid insults to be absorbed by the core, but also providing good separation and a significantly reduced amount of liquid or urine rewet to the top sheet.